Alkylation process



"Feb. 25, 1947. c. s. KUHN, JR

ALKYLATION PROCESS v Filed July 22, 1944 4 Sheets-Sheet l w. R n @hk n M.NNb @SHQ n mi A nv m l l I i l -l Y www. HH HH\ HMM WW1. HMH 5ML LSwu... HH 2 @k :l :i Il -il s Hugo Il :i :l :I ww SQSNN .QY l l|\ tf il,.i kmwhbvm Ill Il Q n Il: :1| 1mm- N ,MNM .HHM .HINV HH i m l i d RIIPu e LE Qu@ bmo Feb. 2'5, 1947.

Filed July 22, 1944 4 Sheets-Sheet 2 inw@ QZY km ,AR m J0 N MM W m WL mmm T um s/A Frm d MM 0 ci, C g E m ww A w m o 2 w w ,w n 4 Patented Feb.2.5, 1947 2,416,395 ALKYLATION PROCESS om s, Kuhn, Jr., assignments, to

of New York Dallas, Tex., assignor, by mesne Socony-Vacuum Oil Company,Incorporated, New York,

N. Y., a corporation Application July 22, 1944, Serial No. 546,111

4 Claims.

This invention relates .to catalytic alkylation of paramn hydrocarbonswith olefin hydrocarbons. The invention particularly relates to themanufacture of high grade motor fuels by the catalytic alkylation ofnormally gaseous isoparaillns with propylene, and is acontinuationin-part of my copending application Serial Number 320,097,led February 21, 1940.

Catalytic synthesis of high grade .motor fuels by means of alkylation ofsuitable parafilns with suitable olefins has assumed increasingimportance in the recent years. By proper choice of parailns andolefins, as for example, isobutane and a butylene, and by carrying outthe process under proper conditions, the reaction can be controlled togive directly high yields of products composed of iso-octanes orparaillnic compounds approximating iso-octanes in structure and emciencyas motor fuel. The process is of particular importance since gaseousproducts containing suitable isoparafns and olefins are commonby-products in the petroleum art.

Various catalysts have been proposed for this alkylation reaction.Sulphuric acid, the use of which for catalytic alkylation is disclosedin U. S. Patent 2,169,809 to Jacque C. Morrell has proven commerciallysatisfactory. More recently, hydrofluoric acid has found widespreadacceptance as an especially useful alkylation catalyst, and the use ofthis catalyst for alkylation is disclosed in U. S. Patent 2,267,730 toA, V. Grosse et al. and in my copending application above referred to.Hydrofluoric acid has many advantages for the alkylation of isoparamnsamong which may be mentioned its low viscosity as compared withsulphuric acid, rendering agitation of the hydrocarbon-acid catalystmixture more economical, and its nonoxidizing character as compared withsulphuric acid, enabling its use over a wider temperature range and withless undesirable side reactions. Additionally because of the low boilingpoint and thermal stability of the acid at normal and moderatelyelevated temperature levels, hydroiluoric acid y be readily purified forcontinued reuse in, an alkylation between process without decomposition.Furthermore, hydrogen fluoride is of a simple, stable composition andits preparation and use present no particular dimculties. It can behandled, for example, in ordinary steel or stainless steel equipment.

The alkylation reaction is generally conceived of as a direct unionbetween a molecule of isoparailin and a molecule of an clen to yield amolecule of branched chain paramn having a number of carbon atomscorresponding to the uct. Furthermore,

total number of carbon atoms in the original isoparailln plus the numberof carbon atoms in the olefin, thus In the ordinary isobutane-butenealkylation, which has become a highly important commercial process forthe production of aviation gasoline, it has been observed that a widevariety of hydrocarbons are found in the ultimate product, but thesehave been predominantly octanes and the explanation of the reaction as adirect reaction or union of isoparamn with olefin has seemed sound.Since butene exists in three isomeric forms, i. e., butene-1, butene-2,and isobutene, a plurality of major product isomers was to be expected.or nonanes and heavier were explained as resulting from secondaryreactions such as isomerization and reforming occurring within theoriginal octane products. These explanations seemed to t the facts inthe case of butene alkylation.

The alkylation of other oleiins such as propylene and pentene whilepossible with sulphuric. acid and more practicable with hydrouoric acid.as will be hereinafter pointed out more fully, were considered but neverexperimented with or studied in detail largely because it appeared thatthe hydrocarbon products were inferior to butenes alkylate.

If the considerations discussed above were sound as explaining themechanics of what has been considered alkylation, then in the alkylationof isobutane with propylene, heptanes should be the major product withminor amounts of various hexanes and lighter, and octanes and heavier. Ihave found, however, that octanes may be fully as important products ofpropylene alkylation as heptanes, and that, for example, the octane2,2,4- trimethyl pentane ,may constitute as much as about 40 mol percentof the entire alkylate prodit is dilcult to ascribe this high octaneformation to what are usually reterred to as reforming ordisproportionation reactions, i. e.,

ZC'IHisZI-ZCeHu-l-CsHis since the amount of hexanes is nowhere nearcomparable.

Without intending to limit the invention to any theoreticalconsiderations, I believe that a Other octanes and heptanes and lighterAlkylation reactor 6 is turned through valvedl line 23 alkylationreactor.

tion reactor through line 32.

v column 3| are then pumped depropanizer 34. Residual traces ofhydrofluoric 3 possible explanation of the formation of these octaneslies in the reactions expressed by the following equations:

The reactions involved are thus seen to be hydrogen-exchange reactions(Equations 1 and 4), accompanied by what has been commonly considered asalkylation (Equation 2) and/ur polymerization (Equation A3). 'I'heoccurrence ofthese phenomena. in'conventional butene-isobutanealkylation would not attract attention since the olefin and thelisoparailin have thesame number of carbon atoms, and hence all primaryproducts would have eight carbon atoms. And, since the butene feedstocks contain isomeric butenes, product variations are expected. If,however, as appears to be the case, alkylation is a much more complexreaction than has been heretofore" supposed, then even in'v the simplecase (from the standpoint of reaction mechanism) of propylenealkylation, a wide variety of products becomes possible even fromprimary reactions. and control of reaction conditions in alkylationreactions in order to obtain desired products is imperative. This istrue since, as is well known, the octane rating, volatility, leadsusceptibility,1etc., of the various 'gasoline boiling hydrocarbons varywidely.

In order that my invention may be better understood and that certainterms used in the description thereof more clearly defined. thealkylation of propylene with isobutane will be described in commotionwith the flow sheet in Figure 1 of the drawings.

Referring to Figure 1, isobutane is introduced through line l providedwith a suitable control valve 2 where it is admixed withrecycleisobutane, obtained in the manner hereinafter described, returnedthrough line 3, and propylene feed introduced through line 4 at a rateregulated -by control valve 5 into alkylation reacton 6.

diagrammatically illustrated as being of the reaction loop type whereincirculation is provided by pump 'l and temperature control is effectedby diverting a suitable portion of the circulating reaction mixturethrough cooler 8 by ow regulating valve 9. Any suitable alkylationreactor and temperature control system could obviously be substitutedfor that diagrammatically illustrated. A portion of the reaction mixtureis continuously withdrawn through line at a rate regulated by controlvalve 2i and sent to separator 22 for gravity separation of hydroiiuoricacid catalyst from the hydrocarbons of the alkylation reaction mixtureemulsion. Recycle. acidcatalyst is withdrawn from the lower portion ofseparator 22 and reby pump 24 to the Make up hydrofluoric acid isintroduced as necessary through valved line t 25 to thehydrouoric acidrecycle line 23. The hydrocarbon phase from the separator is takenoverhead through line and sent to a hydroiiuoric acid stripping column3| where the major portion of dissolved and suspended hydrofiuoric acidcarried over in the hydrocarbon phase is vaporized overhead and returnedto the alkyla- The substantially hydroiluoric acid free bottoms fromstripping through line 33 to acid and organic uorides contained in thebottom's from stripper 3| may be removed by chemical treatment, as withbauxite, prior to introduction of the hydrocarbons into depropanizer 34,if desired. Propane formed in the reaction or introduced with the freshhydrocarbon feed together with any unreacted propylene are removedoverhead through line 36 for further treatment. The depropanizedhydrocarbons are then pumped through line to deisobutanizerl 4| fromwhich unreacted isobutane and any isopropyl fluoride formed are takenoil overhead via line I2, condensed in condenser 43, and returnedthrough line 3 to the alkylatlon reactor as hereinbefore described. Thebottoms from deisobutanizer 4l which consist principally of the alkylatehydrocarbon product together with any normal butane introduced with theisobutane feed or formed in the reaction are then/pumped to stabilizervia line 46. The stabilized alkylate gasoline may be recovered from thebottom portion otrstabilizer l5 and taken oi through line".

Many modifications in the product fractionation and recovery system willbe readily apparent to those skilled in the art, and the foregoingdescription thereof should be considered as illus.- t'rative only of anoperative procedure.

The following terms as used hereinafter have the signincance indicatedbelow:

The "external isoparaflin-oleiln ratio" refers to the mol ratio of freshisobutane feed (in line average residence time ofthe hydrocarbons in 1)plus recycle isobutane (in lineV 3) to the fresh olefin feed (in line4).

'The residence time of thehydrocarbons is an arbitrary valuerepresenting theoretical contact with the catalyst and equals the totalvolume of hydrocarbons in the alkylation reactor including the coolerdivided by the volume ot total feed hydrocarbons per minute (the sum ofthe feed in lines 1, 3, and 4). This does not include the hydrocarbonsin contact with catalyst in the line leading to the acid settler (line20) nor in the settler itself; however, the relative amount in theformer case is small, and in the latter case the additional contactingfor the maior part of the hydrocarbons is of short duration (of theorder of a few seconds).

The acid-hydrocarbon ratio" refers to the volume ratio of acid catalystto total liquid h ydrocarbons in the alkylation reactor.

As mentioned above I have found experimentally that a Wide variety ofreactions is involved in alkylation, which includes besides the directunion of isoparafiln and olefin such reactions as hydrogen exchange,polymerization, isomerization and disproportionation. Since thesereactions do not all proceed at the same rate and their respective ratesare probably aected in different degrees by changes in temperature, Ihave realized the possibility of controlling the extent to `which thevarious reactions occur in order that particularly desirable hydrocarbonproducts may b e formed. fore, the object of my invention is to properlycorrelate the reaction conditions for the hydrouoric acid alkylation ofpropylene so as to produce superior products containing relatively largeamounts of high octane rating and otherwise desirable hydrocarbons. Asused in the foregoing sentence and henceforth throughout thisspecication, unless otherwise indicated, by the term alkylation I referbroadly to the formation of predominantly saturated gasoline boilinghydrocarbons by a reaction, regardless of the rements in the series wereaction mechanism, involving the consumption of isoparafiin and olefinlin approximately equimoiar quantities, i. e., within 25 to 30%.

In order to more fully understand my invention reference should be madeto Figures 2, 3 and 4, which represent a plot of product distributionversus temperature obtained in a series of experiments conducted at aconstant average residence time of 135 minutes, a constantacid-hydrocarbon ratio of 0.20, and a constant externalisobutane-propylene mol ratio of 5. The expericonducted batchwise with arate of addition of olefin of 6.82 104 grams of olefin per gram ofisobutane p er minute.

Figure 2 shows the variation in quantity of 2,3- dimethyl pentane withtemperature under the reaction conditions outlined above on the basis ofC to Ca fraction of the total alkylate, and on the basis of totalalkylate.

Figure 3 shows the variation in quantities of 2,4-dimethyl pentane and2,2,4-trimethyl pentane with temperature on the basis of the Cs to Cafraction and on the basis of total alkylate.

Figure 4 shows the variation in quantities of isopentane, hexanes,octanes other than 2,2,4- trimethyl pentane and C9 plus hydrocarbonswith temperature on the basis of total alkylate.

Although 2,2,4-trimethyl pentane is a highly desirable hydrocarbon, and,as may be seen from Figure 3, the process may be operated to produceover 30% (nearly 40% Ca fraction) of this hydrocarbon in the totalalkylate product, I prefer to operate a propylene alkylation processutilizing the ratio of 2,3-dimethyl pentane to 2,4-dimethyl pentane asthe factor controlling the selection of operating conditions. This isbecause '2,3-dimethyl pentane is a much more desirable hydrocarbon than2,4- dimethyl pentane from the standpoint of a superior AFD 3C, richmixture rating. Therefore, even though high ratios of 2,3-dimethylpentane to :L4-dimethyl pentane do not generally correspond to a highyield of 2,2,4-trimethyl pentane, the elimination of the formation of asubstantial quantity of a low performance constituent on a rich mixturebasis is of primary importance.

Temperature, however, is not by any means the sole factor influencingthe nature of the propylene alkylation reaction. Other variables alsoinfluence the reaction particularly residence time, and as the result ofextensive experimentation I prefer to utilize what I shall hereinafterterm an alkylation factor to correlate the variables in alkylation. Inaddition to temperature and residence time which are the main variablesin determining the Vcourse of the reaction, other variables such as' theacid-hydrocarbon ratio, degree of contacting or'mixing of catalyst andhydrocarbons, olefin concentration in the reaction zone and externalisobutane-propylene ratio affect the degree of alkylation and nature ofthe product. These other factors, however, exert but a relatively minorinfluence upon the composition of the C5 to Cs fraction so long asvigorous agitation is employed and the other variables lie within theranges which are usual for commercial hydrofiuoric acid alkylation.

As mentioned above, 2,3-dimethyl pentane is much preferred to2,4-dimethyl pentane, and I therefore prefer to control the propylenealkylation to produce a minimum of the latter heptane. The reason forthe undesirability of 2,4-dimethyl pentane will be readily apparent by astudy of the octane ratings (A. S. T. M.) and performance numbers ofthese hydrocarbons.

on the basis of the C5 tov (compared to the Therefore in order toproduce a high quality alkylate from propylene, conditions should bechosen such that the relative amount of 2,3-dimethyl pentane is of theorder of about five times greater than the amount of 2,4-dimethylpentane. Preferably the amount of 2,4-dimethyl pentane in the totalalkylate is held to a value of not more than about 5 to '1%. While thismay be readily done by conducting the reaction under conditions suchthat it is very incomplete, i. e.. a low yield of alkylate on the basisof propylene consumed, it is obvious that the desired hydrocarbondistribution should be obtained at little or no sacrifice in yield. Ihave found that in order to obtain the desired product distribution witha yield of total alkylate of at least about on the basis of weight ofpropylene converted theoretical yield of 238%) the alkylation reactionshould be controlled so that the value for the alkylation factor lieswithin the range of from 20.8 to 22.1 and preferably within the range21.2 to 21.9, Where the alkylation factor where T=Temperature in degreesKelvin =1Res1dence time in minutes At values for A of less than about20.8 an execssive amount of 2,4-dimethyl pentane and propane are formedand the production of 2,3-dimethyl pentane drops to an undesirably lowvalue. At values for A in excess of 22.1, the alkylation reaction isincomplete either because the residence time is too short, or thetemperature is too low, or both. Within values for A as set forth above,2,3-dimethyl pentane'represents the major constituent of the totalalkylate product, and within the preferred range this hydrocarbonrepresents more than about 90% of the heptane fraction while2,4-dimethyl pentane is but a minor alkylation product.

In order to illustrate the manner in which the residence time and thetemperature of the reacv tion mixture should becorrelated to attain thedesired high 2,3-dimethyl pentane production and high yield of alkylateproduct on the basis of reactants consumed, and to avoid the undesirableproduction of propane, 2,4-dimethyl pentane and Cn plus hydrocarbons,Figure 5, which represents a plot of residence time against reactiontemperature, depicts in the shaded area the desirable operating range inaccordance with my invention and in the cross hatched area the operatingrange preferably employed.'

As mentioned previously, the permissible conditions are defined by thelimits for A of between 20.8 to 22.1, with preferred values lyingbetween 21.2 and 21.9. Other considerations and practicable operatingconditions impose othe1` limitations upon the alkylation conditionsused. Temperatures below 10 C. should not be used, not

only because of the extremely long residence time audace er than 500minutes are impracticable, and preferably residence times of are used.

Likewise temperatures of. about 40 sent an upper limit. This is becauseof the fact that at the extremely low residence time permissible to meetthe required A value, high rates oi less than 300 minutes 'reactionimpose impracticable requirements on reactor design and heat transferequipment, and

permissible range.

C. should preferably be used. Within -these` temperature limitations,practical considproper A value in order'that a superiorpropylene-isobutane alkylate may yield.

In order that .the results be produced in high obtained by operating apropylene-isobutane alkylation using hydrouoric acid as the alkylationcatalyst may be C. repremore fully understood. I have tabulated below,l

the eect of temperature and residence times at various values for A uponthe 2,3-dimethy1 pentane content of the heptane fraction and upon theyield of total alkylate. The ratio of 2,3-dimethyl pentane to2,4-dimethyl pentane may be very nearly determined from' the valuesgiven since the amount of other heptanes is very small, of the order offrom 1 to 2% of the total alkylate over the range of conditions ofinterest. The results tabulated represent a selection of typicalexamples and, where yield ranges are indicated, represent variations inresults of several experiments obtained at the conditions indicated.Largely these variations are believed to be due to diilculties inmaintaining. temperature levels constant and olefin feed rates uniformin Small l scale batch and continuous operation, particu- 1 larly at theshorter residence times.

am i ist?. i si..

2,. yie d o o K C minutes in C, fraction alkylate 265 -8 l 135 22. 4 95.7 7 271 -2 135 21. 9 96. 0 130450 276 3 135 21. 4 9?. l 209 283 l 13520. 9 88. 6 21o-220 288 15 135 20. 4 70. 5 2l8225 298 25 135 I9. 7 52. 7215-225 I 30S 35 135 19. 0 49. 3 222 283 l0 8 0 92. 5 l 10-145 29s 25 s/o 80.9 lss-n4 31s 4o s 2o. 1 e4. 7 19E-21o 278 5 35 21. 8 94. 5 185-292289 16 4. 5 21. 8 97.. 5 2195-101 297 24 2. 2 21. 6 91. 7 18o-195 297 24(i0 20. 1 49. 8

In order to illustrate the relationship between the value of thealkylation factor and the relative Ex. 1 Ex. 2 Ex. 3

Tem .,C -2 6.0 10.0 Resi ence time in minutes 140 35 4.5 Productdistribution, weight percent:

Pentsnes 0.36 3. exanes l. d2 2. 2,4-D. M. P 4. 22 6. 2,3-D. 7l. l0 75.2 2,4-T. M. P 16. 25 8. :hgh 6.45 a. Percent M. P 94. 5 92. 7

From the foregoing table it is apparent that at a constant A value theamount of 2,3-dimethyl pentane inthe total dimethyl pentane fractionremains substantially uniform. Y Other heptanes than the dimethylpentanes are included in the values given for these two hydrocarbons,since they are distributed therebetween and represent but very small anddiilicultly separable fractions.

In carrying out the experiments` from which the data tabulated abovewere obtained, a continuous reaction system similar to'that illustratedin the flow sheet is satisfactory except that the continuousfractionation system can be eliminated and a representative sample ofthe hydrocarbon eiiluent from the separator after suitable stripping andstabilizing can be analyzed for the representative hydrocarbonconstituents. Operating in this manner the lack of'contlnuous isobutanerecycle may be compensated for by an increase in the amount of isobutanefeed. Continuous alkylation gives most satisfactory results for theshorter residence times particularly. since an attempt to get shortresidence time in batch operation results in high and nonuniform olenconcentrations. For experimental work conducted at longer residencetimes, i. e., upwards of thirty minutes batchwise operation issatisfactory and permits the use of quantities of materials more readilyhandled. 'I'he method of conducting a batch experiment is illustrated bythe following example. j

'185 parts by weight of liquid isobutane are mixed thoroughly with 300parts by weight of essentially anhydrous hydroi'luoric acid. To thisagitated mixture, 114 parts by weight of propylene (95% propylene, 5%propane) are added continuously over a period of four hours. During theaddition of olefin, the temperature is maintained at about 8 C.(A=22.1), and after completing the addition of olen, agitation isdiscontinued and the two liquid phases separated. The hydrouoric acidphase is then withdrawn as the bottom layer and the hydrocarbon phase Iis washedwith water, dried and fractionated.

The material boiling above 27 C. in the hydrocarbon phase is recovered.

understood that in practical commercial operations the use of thesehydrocarbons contaminated with other hydrocarbons is contemplated.Ordinary streams of isobutane contaminated with normal butane and minorquantities of other hydrocarbons from any source may be used. Likewisethe propylene feed stock employed need not be pure, and may be admixedwith considerable proportions of propane for example. Other olens mayalso be present in small amounts up to 5 or l0 mol percent or slightlyhigher on the basis of total olens. The process conditions outlinedherein, however, are not intended for application to olen mixtures sincethe reaction variables herein controlled are controlledin accordancewith the attainment of a desirable propylene alkylate and not otheroleiinic alkylates. Likewise the eiiect of large amounts of otherhydrogenacceptors than propylene might well substantially alter theconditions herein found desirable.

The foregoing description of my invention is illustrative only of themode of hydrofluoric acidpropylene alkylation, and the invention shouldnot be construed as limited except as required by the appended claims.

I claim:

1. Process for the production of alkylate hydrocarbon fuel of highoctane rating and consisting predominantly of 2,3-dimethyl pentane whichcomprises reacting propylene with isobutane in ,the substantial absenceof other unsaturated hydrocarbons and under alkylating conditions ofisobutane to propylene concentration ratio in the presence ofhydrofluoric acid as the effective catalytic agent in a reaction zone,maintaining a temperature of from about C. to about +40 C. in thereaction zone, correlating the residence time of the hydrocarbons in thereaction zone '.vith the temperature to give a factor of alkylation inaccordance with the formula where T=Temperature in degrees Kelvin=Residence time in minutes A=The alkylation factor and represents avalue between 20.8 and 22.1.

2. Process for the production of a'lkylate hydrocarbon fuel of highoctane rating and consisting predominantly of 2,3-dimethyl pentane whichcomprises reacting propylene with isobutane inwhere T=Temperature indegrees Kelvin =Residence time in minutes A=The alkylaton' factor andrepresents a value between 21.2 and 21.9.

3. Process for the production of alkylate hydroy carbon fuel of highoctane rating and consisting predominantly of 2,3-dimethyl pentane whichcomprises reacting propylene with isobutane in the substantial absence oother unsaturated hydrocarbons and under alkylating conditions ofisobutane to propylene concentration ratio in the presence oihydroiluoric acid as the effective catalytic agent in a reactionzone,maintaining the hydrocarbons and acid catalyst in contact in saidreaction zone for a residence time of from 0.33 to 500 minutes,maintaining -a temperature of from about 10 C. to about +40 C. in theAreaction zone, correlating the residence time 0f the hydrocarbons in thereaction zone with the temperatureto give a factor of alkylation in'accordance with the formulawhere T=Temperature in degrees Kelvin=Residence time in minutes A=The alkylation factor and represents a.value between 20.8 and 22.1.

4. Process for the production of alkylate hydrocarbon fuel of highoctane rating and consisting predominantly of 2,3-dimethy1 pentane whichcomprises reacting propylene with isobutane in the substantial absenceof unsaturated hydrocarbons and under alkylating conditions of isobutaneto propylene concentration ratio in the presence of hydrofluoric acid asthe effective catalytic agent in a reaction zone,lmaintaining thehydrocarbons and acid catalyst in contact in said reaction zone for aresidence time ofv from 1.0 to 300 minutes, maintaining a temperature offrom about 0 C. to about 30 C. in the reaction zone, correlating theresidence time of the hydrocarbons in the reaction zone with thetemperature .to give a factor of alk'ylation in accordance with theformula where represents a value REFERENCES CITED The followingreferences are of record in the ille of this patent:

UNITED STATES P ATENTS Number Name Date 2,267,730 Grosse et al. Dec. 30,1941 2,322,800 Frey June 29, 1943

